This invention relates to monolithic integrated circuit structures. More particularly, it is concerned with methods of fabricating complementary metal-oxide-silicon (CMOS) integrated circuit structures.
In integrated circuit structures polycrystalline silicon is frequently used to make ohmic connections to underlying active regions of single crystal silicon. Such polycrystalline connections are particularly useful when employed in conjunction with shallow junction devices because metallization techniques might produce metallic spikes which short out the junction.
In order to obtain proper ohmic connection, the polycrystalline material must be of the same conductivity type as the region of the single crystal material which it contacts. That is, N-type polycrystalline material must be used to contact N-type regions and P-type polycrystalline material must be used to contact P-type regions. Thus, for CMOS structures which have active regions of both N and P-type material both N and P-type polycrystalline material must be employed. A rectifying junction is formed where the two types of polycrystalline material meet. The rectifying junctions must be shorted out by overlying conductive material.
Thus, it is desirable that techniques of fabricating integrated circuit structures of the CMOS type permit the utilization of polycrystalline connections of both conductivity types together with suitable metallization to short out junctions. In addition the techniques should permit precise control of the channel regions and of the gate electrode structures of the MOS field effect transistors (FET's).